It took me awhile this season to figure out what was causing this. Most of the time we would get to the river the night before, take the boat out the next day, clean it, put it in the garage, and then leave.

Several times though, we would hang out at the house after putting the boat up or even stay the night and the smoke detectors would randomly go off.

We had replaced several of them before I realized that if I didn't plug in the charger for the boat (Xantrex 40A TruCharge 2), the smoke detectors would not go off. The smoke detectors are hard wired, FYI.

When you charge your battery's they will gas off. If your battery's charging sets your smoke detector off and your not smoking out the garage ( over charging) your charger is a high quality smart charger so i would say over charging is most likely Not the problem . I would say Mabey your smoke detector is faulty and you should change it out. They can become clogged with dust and partials that can help give you a false alarm.

"The smokes must be picking up heat on the 110 line. Your garage breaker is probably only a 15 amp which would cause to much draw on the line and cause it to heat up. You can check that and see if it is only a 15 amp you should change it out to a 30, especially if you have other things like refrigerators or freezers."

According to the owners guide that model charger pulls 7.7 amps at 120 VAC. You should not be over amping a 15A circuit. Furthermore, if you are plugging the charger in the garage and the smokes in the house are going off odds are they aren't even on the same circuit which would definitely not have anything to do with the charger being plugged in.

If they do happen to be on the same circuit, since this happens within minutes of the charger being plugged in maybe the smokes see a voltage drop causing them give off false alarms. I would verify if the charger and smokes are on the same circuit. If they are then I would test to see if there is a significant voltage drop at the smokes and check the operating range of them.

I'm an EE and I work in the solar power space so I understand the electronics of the converter. Converting AC to high power DC can be dirty business from a power quality standpoint. That said, it is still a most unusual situation. It is possible the Xantrex is causing some distortion on the AC sine wave that is tripping up the smoke detector electronics. Did you replace your smokes with the same brand?

You might try adding a 50-100' 14awg extension cord to introduce some inductance into the power path if you have one lying around. This could be enough to buffer the distortion so the smokes don't trip. No guarantees but it's easy to try.

Alternatively you could call Schneider (parent company of Xantrex). They might be able to help you out. If you don't get anywhere with them go ahead and PM me, I can bring it up with my Schneider rep and ask him to ask one of his techs.

One more thing, make sure the neutral wire at your main service and sub-panel is good and tight.

I'm an electrical contractor and have installed or replaced 1000's of smoke detectors. I've never come across a situation like you describe. The first thing I would do to trouble shoot your problem is try plugging the charger in on a different circuit than the smoke detectors and see if the problem goes away. That would rule out any "interference" problems. Also, NEVER put a 30 amp breaker on a 15 amp circuit! That wire is only meant to handle 15 amps. You're asking for a fire if you install a breaker that is larger.